StringBuilder

The StringBuilder class in VB.NET optimizes and improves common String operations. Appending, replacing and inserting are faster.

With ToString, we can convert our data back into a String. This operation is optimized to avoid copies. With StringBuilder we have many built-in optimizations.

Append example

We see a program that declares a new StringBuilder. Then it uses a simple For-loop and appends integers and 1-character strings to it.

Imports System.Text

Module Module1
    Sub Main()
        ' Create StringBuilder and append to it in a loop.
        Dim builder As New StringBuilder()
        For i As Integer = 0 To 2
            builder.Append(i).Append(" ")
        Next
        Console.WriteLine(builder)
    End Sub
End Module
0 1 2

AppendFormat

Next we use AppendFormat. This function receives a format string, usually with substitutions such as {0}, and parameters to fill those substitutions.

Imports System.Text

Module Module1
    Sub Main()
        ' StringBuilder declaration.
        Dim builder As New StringBuilder
        Dim number As Integer = 1
        builder.AppendFormat("R: {0} ({1}).", "ABC", number)
        ' Print the resulting string data.
        Console.WriteLine(builder)
    End Sub
End Module
R: ABC (1).

Replace

This example creates a StringBuilder with the constructor. Then it calls Replace() to replace one substring with another. Performance is good. No string temporaries are created.

Imports System.Text

Module Module1
    Sub Main()
        Dim builder As New StringBuilder("Initialize the StringBuilder.")
        builder.Replace("the", "my")

        Console.WriteLine(builder.ToString)
    End Sub
End Module
Initialize my StringBuilder.

Replace, all instances

The Replace() Function does not just replace the first instance of a string it finds. It changes all of them, no matter how many there are.

Imports System.Text

Module Module1
    Sub Main()
        Dim builder As New StringBuilder("I see a cat, and the cat sees me.")

        ' Replace all instances of substring.
        builder.Replace("cat", "dog")
        Console.WriteLine("RESULT: {0}", builder)
    End Sub
End Module
RESULT: I see a dog, and the dog sees me.

For-each

Here we use StringBuilder in a For-Each loop. Whenever we see Strings being appended in a loop, consider StringBuilder. It can improve runtime performance.

Imports System.Text

Module Module1
    Sub Main()
        ' String array for use in loop.
        Dim items As String() = New String() {"Indus", "Danube", "Nile"}

        ' Initialize new StringBuilder.
        Dim builder As StringBuilder =
            New StringBuilder("These rivers are cool:").AppendLine

        ' Loop over each item in Array.
        For Each item As String In items
            builder.Append(item).AppendLine()
        Next

        ' Write result.
        Console.WriteLine(builder.ToString)
    End Sub
End Module
These rivers are cool:
Indus
Danube
Nile

Insert

This modifies a StringBuilder at the specified index. Here I specify the index 1, so the String literal is inserted after the first character in the buffer.

Imports System.Text

Module Module1

    Sub Main()
        Dim builder As StringBuilder = New StringBuilder("A cat")
        Console.WriteLine(builder)

        ' Insert this string at index 1.
        builder.Insert(1, " fluffy")

        Console.WriteLine(builder)
    End Sub

End Module
A cat
A fluffy cat

Remove

This erases characters from a StringBuilder and collapse those following it. In this example, I remove four chars starting at index 1.

Imports System.Text

Module Module1

    Sub Main()
        Dim builder As StringBuilder = New StringBuilder("A big dog")
        Console.WriteLine(builder)

        ' Remove character starting at index 1.
        ' ... Remove 4 characters.
        builder.Remove(1, 4)

        Console.WriteLine(builder)
    End Sub

End Module
A big dog
A dog

Benchmark

In appending, StringBuilder is faster than String. Consider this benchmark: we want to append 3-character string (abc). We compare StringBuilder and String.

Imports System.Text

Module Module1

    Sub Main()

        Dim m As Integer = 100000

        ' Version 1: use StringBuilder.
        Dim s1 As Stopwatch = Stopwatch.StartNew
        For i As Integer = 0 To m - 1
            Dim builder As StringBuilder = New StringBuilder
            For x As Integer = 0 To 99
                builder.Append("abc")
            Next
        Next
        s1.Stop()

        ' Version 2: use String.
        Dim s2 As Stopwatch = Stopwatch.StartNew
        For i As Integer = 0 To m - 1
            Dim str As String = ""
            For x As Integer = 0 To 99
                str += "abc"
            Next
        Next
        s2.Stop()

        Dim u As Integer = 1000000
        Console.WriteLine( s1.Elapsed.TotalMilliseconds.ToString("0.00 ms"))
        Console.WriteLine( s2.Elapsed.TotalMilliseconds.ToString("0.00 ms"))
    End Sub

End Module
 156.04 ms,    StringBuilder Append
1020.00 ms,    String concat

Performance advice

My research shows that appending two or three strings in a loop is faster than using StringBuilder. But using StringBuilder is faster for more than four iterations.

HtmlTextWriter

HTML syntax uses lots of quotes and brackets. We can write HTML markup directly, without dealing with syntax: check out HtmlTextWriter.

As developers, we will require StringBuilder in many applications. It is an excellent performance optimization. Often, we use StringBuilder in For-Each loops.